G4URH - Modifications for the Kenwood TS-870 <br>at your own risk.

 Aerial Calculations 
 Balun Theory 
 Beacon Listings Vhf Uhf 
 Calculating Dbm 
 Calculating Freq 
 Coax Cable Spec 
 Ic821h Mods 
 Kenwood Ts2000 
 Kenwood Ts890 
 M0ebj S Match 
 Prefix List 
 Q Codes 
 Radio Mods 
 Uk Repeater 
 Watt Converter 
Go to Home Page : Amateur Radio Help

G4URH - Modifications for the Kenwood TS-870
at your own risk.

For other Modifications visit: Radio Modifications
and thanks for this information.


  • TS870S first figure of the serial numbers linked to year of manufacture as follows:

  • This is how it works:
  • 7 = 1995
  • 8 = 1996
  • 9 = 1997
  • 0 = 1998
  • 1 = 1999
  • 2 = 2000
  • 3 = 2001
  • 4 = 2002
  • 5 = 2003
  • 6 = 2004

  • Frequency expansion for the TS-870S
    Here is your chance to prove how adept you are at microsurgery. This mod will enable the TS-870S to transmit on MARS, CAP and othe frequencies.

    1. Remove top and bottom covers.
    2. Remove the top screw from each side of the front panel assembly.
    3. Carefully rotate the front panel forward to gain access to the control board(x53-3560-11 a/4). This board is mounted vertically against the body of the transceiver. It is not the board that is mounted in the front panel assembly.
    4. Locate and remove resistor R244 from the control board. R244 is below IC12 ROM and above IC23. There are two chip resistors, one on top of the other -carefully remove or break the top one..it is easily fractured -that's R244.
    5. 5. Reassemble and then perform the cpu reset by holding the A=B button depressed as power is turned on.

    TS870 DSP XCVR specs

    The Kenwood TS870 radio has a fully digital signal path. All filtering, both in terms of width and noise reduction, is acheived digitally, so there are no optional analogue filters!

    Also built in as standard are a K1 logikeyer for the dedicated cw operator, an auto atu which covers both tx and rx, plus an RS-232 adaptor internally.

    Third party windows based control programs are available.

    By applying the best of it's DSP technology, Kenwood has succeeded in developing the TS870S, a new gerneration of HF SSB transceiver that offers superior digital interference reduction as well as receiver performance of a quality hitherto impossible using the conventional analogue circuitry.
    New HF transceivers based on this design concept are collectively called the "Intelligent Enhanced Communications System". (AA1)

    HF DSP for post-IF signal processing:
    Digital RX Filters: The TS870s features post-IF digital filters for ALL modes - SSB,CW, AM, FSK and FM, a World first!! offering precise performance that is unobtainable with analogue circuits.
    Bandwidth of the digital filters can be optimised in various working conditions. You are now also free from struggling to put in the optional IF filters, thanks to the new razor sharp digital filters.

    Hi Cut: 1.4 - 6.00khz (12 steps)
    Low cut: 0 - 1000hz (10 steps)

    CW MODE:
    VBT: 50 - 1000hz (6 steps)
    SHIFT: 400 - 1000hz (13 steps)

    FM MODE:
    VBT: 5 - 14khz (6 steps)

    AM MODE:
    Hi Cut: 2.5 - 7khz (6 steps)
    Low Cut: 0 - 500hz (4 steps)

    VBT: 250 - 1500hz (4 steps)

    The TS870S is capable of picking out a target signal that is buried in the noise. To accomplish this, it employs the line enhancer method for ssb mode and the SPAC method for cw mode.

    This cancels out the sort of multiple beat interference that can effect reception automatically, which is impossible for analogue circuits.

    This is a filter which, when beat interference is experienced, attenuates only the interfering signal. Should the frequency change, the filter adjusts automatically.
    Thanks to the post-IF DSP, it offers more precise performance than previously possible.

    SELECTABLE TX AUDIO QUALITY & Characteristics:
    3 types of adjustments are possible:

    In SSB and AM Modes, the bandwidth of the bandpass filter can be controlled.

    The speech processor can be adjusted seperately for low, medium and high ranges.

    Equipped with 3 equalisers, high boost, bass boost and comb filter, the TS870S allows the user to select the desired sound quality.

    Thanks to DSP Technology, the quality of signal detection is better than possible with conventional transceivers, in terms of both low distortion and high sound quality.

    ATU that works on both RX and TX!!!!

    Special CW features:
    4 Channel Memory in built.....based on the K1 Logikey*tm:
    2 Key Connectors!
    CW Pitch control between 400 & 1000hz in 50hz steps!

    By adding the DRU-3 unit, up to 60 seconds of continuous digital recording is possible!

    TS-870S S-Meter pin with repeated RX/TX switching

    Kenwood service buletin 10/11/1996

    The transceiver must be in the SSB mode, processor turned on, and AGC set to Slow. Repeated switching between transmit and receive may cause the S-mater to pin full scale. At that time, the receiver will mute for a few seconds.

    Insufficient processing of the AGC circuit.

    Replace the three EPROMs on the TX-RX board with the new ones listed below.

    TX-RX Board X57-4620-00 (2/2)
    Ref. Original P/N New P/N
    IC4 27C256PCJJTE 27C256PCJJTF
    IC5 27C256PCJJUE 27C256PCJJUF
    IC6 27C256PCJJVE 27C256PCJJVF

    1. Remove the bottom cover of the TS-870S

    2. Remove the shield that covers the TX-RX board which is located on the right side of the bottom of the transceiver.

    3. Carefully remove IC4, IC5, & IC6 from their sockets and replace them with the new parts listed above.

    4. reset the transceiver by holding the [A#B] key depressed as power is turned on.
    1. Make sure the pins of the new EPROMs are properly aligned before insertion. New EPROMs tend to have the pins spread aout wider than the socket. The pins can be beat in by pressing each side of the EPROM against a static free work surface.

    2. Avoid touching the EPROM pins. Graps the device from the top and bottom epoxy body ands between thumb and forefinger.

    3. Avoid inserting the EPROMa backwards.
    Only perform this change on units received for service with the exact sympthon listed above.
    Use service codes (8): 18(B): X57-4620(P): IC4(C):91 on WSR.
    Time required for this alignments is 15 minutes.

    TS-870S Receiver circuit changes

    Kenwood service buletin

    The following provides a more useable range af the RF attenuator by re-allocating stage gain at the first and third IF. This change allows the use af less front end attenuation, allowing you to hear the desired signal while reducing interfering signals during CW contests and pine ups.

    This change requires advance surface mount soldering equitment that is rated for CMOS circuits. It also requires farmiliarity with advanced surface mountesoldering techniques. If you do not have the proper equitment or knowledge, seek qualified assistance.

    Required Parts:
    RF PCB:
    R157         1,8K  to  560      RK73FB2A561J
    R160,161     2,2K  to  1K       RK73FB2A102J
    R164         1.5K  to  560      RK73FB2A561J
    R169         1K    to  330      RK73FB2A331J
    L76,79       3.3u  to  0        R92-0670-05
    TX-RX PCB:
    R332         2.2K  to  6.8K     RK73FB2A682J
    C340         .022u to  .01u     CK73GB1C104K
    VR1          470   to  3.3K     R12-6737-05 (optimal)

    1. Remove the bottom cover and shields anclosing the RF board and TX-TX board.

    2. Replace L76 and L79 on the component side of the RF board.

    3. Replace C340 and R332 on the component side of the TX-RX board.

    4. Access the bottom side of the RF board and replace R157, 160, 161, 164 and 169.

    5. Perform S-Meter alignment step 8, on page 95 of the Service Manual. If you cannot obtain "05" of the display, replace VR1 on the TX-RX boardwith the part listed above.

    With the exception of C340, this change was incorporated into production from S/N 801XXXXX, C340 was change at S/N 807XXXXX.

    Time required to perform this change is 1 hour or less.

    Making super radio out of TS-870

    I loved the TS-870 when I first got it. Size is ideal for expedition radio, light weight, fits in carry on luggage. Features and computer controls are excellent, until I used it in the contest on 160m. Bloody thing got overloaded with signals 4 kHz away. Everybody was QRMing me! What a piece of blinking junk! Liking the radio otherwise I inquired at Kenwood about the problem of overload. They came up with modification to remedy the gain distribution in the RF and mixer stages, which was implemented in later production models. After I received the service manual, I started to dig into the radio and came up with few more improvements.

    Earlier production units before S/N 801xxxxx had problem with front end overload and consequent distortion and crossmodulation in the later stages, including DSP, especially noticeable on low bands. To remedy that on those earlier units see the Overload Modification.

    There is an absence of 2nd RX antenna switching (Beverages, etc.). When I inquired at Kenwood, they supplied modification instructions that required some drastic modifications, including cutting the traces. When I obtained service manual, I figured very elegant modification using just plug in diode. See 2nd RX Antenna Switching modification.

    Examining the circuits and filtering arrangement, I have found that Kenwood engineers decided to rely on obtaining the selectivity mainly by using the DSP. Theoretically it is great, except when strong signals blow by the mediocre crystal filters used in stock TS-870, they modulate the following stages, including DSP circuits. The biggest improvement that puts this radio one class higher, is to replace the stock 2nd IF crystal filter and 3rd IF monolithic ceramic filter with high quality International Radio or other filters. Any better shaped filters make tremendous improvement to the selectivity, overload and DSP performance. Depending on intended use, you can use 2.7, 2.4 or 2.1 kHz bandwidth filters. I chose 2.1 mainly for contesting purposes. It is possible to use narrower filters for CW operation, but selectivity selection scheme via microprocessor controlled switching makes it complicated and throws the controls off their markings. I found that 2.1 filters work very well even for CW and are significant improvement over stock arrangement. See Filter Modification.

    Overload Modification NOTE: the changes do not apply to radios with S/N 801xxxxx and later.

    Problem: If there is any strong signal in the proximity on the low bands, it will cause crossmodulation and create a "ghost" signal. It may occur in the contest operation or during the pile-up reception.

    A larger power input signal causes the second mixer output, the NB amplifier input, the third IF amplifier input, and the third IF amplifier output to be saturated.

    Change the gain allocation of the IF stage to raise the limit of saturation. This modification will cause almost no deterioration of receiver sensitivity.

    Circuits from the antenna terminal onward:

    Sequence is:
    Antenna, amplifier, mixer, 73.05MHz filter
    Amplifier, mixer, 8.83 MHz filter - noted gain is -10dB (minus 10)
    Amplifier, mixer, 455kHz filter
    Two Amplifiers - noted gain is +10dB (plus 10)

    Replace the following components with (Kenwood part numbers)
    Caution: they are all SMT chips, you need to be familiar with SMT soldering procedures.

    Changes to circuit board XX4-3210 (A/9) RF UNIT
    R1157 : replace 1.8k with 560 (RK73FB2A561J)
    R160, R161: 2.2k with 1k (RK73FB2A102J)
    R164 : 1.5k with 560 (RK73FB2A561J)
    L76, L79 : 3.3uH with 0(zero) (R92-0670-05)
    R169 : 1k with 330 (RK73FB2A331J)

    X57-4620 TX-RX UNIT
    R332 : replace 2.2k with 6.8k (RK73FB2A682J)

    Do not forget to perform the re-adjustment of the S-meter sensitivity after making the modifications.
    Refer to "8. S-meter adj." on P.95 of the Service Manual for how to do it specifically.
    If you cannot adjust the display to "05", even after you follow the steps described in "8. S-meter adj.", change the resistor as instructed below and make the re-adjustment.
    X57-4620 TX-RX UNIT
    VR-1 : 470 ---> 3.3k (R12-6737-05)

    2nd RX Receive Antenna switching modification
    Kenwood TS870 has two antenna jacks ANT1 and ANT2 and external receiver antenna jack (RCA type) that can accommodate external receiver when activated through the program menu. This adds some attenuation to TS870 receiver signals. There is no provision for external receive antenna switching (Beverages, preamp., etc.) When I inquired Kenwood about this option, they sent me modification instructions that required cutting the traces and rewiring the ext. RX connector. When I received my Service manual and had a look at the circuit, I came up with this simple modification:

    Parts needed: 1 diode (any type) I used rectifier diode, generic NTE125

    Step by step instructions:
    1. (In the following references the front panel of the rig is facing you.)
      Remove the top cover.

    2. Remove 7 screws holding the cover over the FILTER and RELAY unit (in the middle) and remove the cover. (Where the ANT1 and ANT2 connectors go.) This exposes two PC boards.

    3. Locate the connector CN301 on the RELAY unit (adjacent to ANT1 and ANT2).
      It is about 1 inch back and 1 inch left from the ANT1 connector and has three wires going to it - two gray, left and one black, right.

    4. Take the diode, clip the leads to about 0.5 inch length, bend them down and form them so they are spaced about 1/8" and parallel (kinda forming letter Y).

    5. Plug the diode into CN301 connector from the top, pushing the diode wires between the plastic housing and the metal contacts of the connector. Cathode (the end with the band marking) of the diode should go to the middle contact (gray wire), the other end to the left contact (gray wire). Make sure that diode makes good contact with terminals of the connector. Black wire should be free.

    6. That completes the modification. Replace the covers, do not pinch the wires going to the antenna tuner!

    Connect your transmit or main antenna to the ANT2 connector. Connect your receive antenna or preamp output to ANT1 connector. Now you can transmit only through ANT2 connector.
    Front panel button ANT now allows you to select ANT2 (receive/transmit on ANT2) or ANT1 (receive on ANT1, transmit on ANT2). Antenna tuner would always see the impedance on ANT2. The way the switching works, whenever you transmit, you will switch ANT2 on transmit, regardless of ANT1 or ANT2 selection. Much better use of connectors than originally devised by Kenwood

    Notes on TS870 usage:
    Normally there is enough gain on the receiver for beverages. In case that you need to use the preamp or preselector, than turn the AIP on TS870 on, and if needed add the attenuators. Try to keep the noise level peaks close to low end of the Smeter scale. Helps with intermods. If using DSP, play with different settings and different levels of AGC setting, it has effect on overall behavior.

    Filter Modification.

    Major improvement in selectivity and DSP performance can be achieved by replacement of 2nd and 3rd IF filters with sharp crystal filters, like from International Radio. The 2nd IF 8.83 kHz filter used in TS870 is the stock Kenwood crystal filter, while the 3rd IF 455 kHz filter is little ceramic Murata filter.

    I have ordered set of 2.1 kHz filters (8.83 and 455) from IR. The modification involves removal of printed circuit boards where the filters are located, unsoldering the old filters. In their place solder short piece of miniature coax to connect new IR filters. IR filters can be mounted between the circuit boards and the metal chassis using double sided sticky tape. Coax from old filter connections is then connected to new filters. Tweaking the matching IF transformers next to the filters ensures proper match and gain.

    Other filters with wider bandwidth can be used also. For contesting I found 2.1 filters to be the best and the mod works very well on CW also. Selectivity improves as well as functions of DSP. Now it is a decent radio, matching those costing thousand(s) more.

    For TS870S is possible have much power with hidden menu you NR+USB and power on you see the hidden menu turn M.CH/VFO.CH more time and you see in the display 100 Watt. Before you must connect a dammy load for 200 Watt.
    The frequency for this mods is 14 MHz on the TS870. Now you push PTT and turn RIT/XIT.
    The power up remember not up 140 Watt after you ruturn with M.CH/VFO.CH turn and when you see EEPRON you push botton UP near M.CH/VFO.CH and after off your TS870.

    Remember: do not adjust the power to more than 140 watt because the final RF will be destroyed!!

    Kenwood TS870S - ALC-Mod.

    When I got the TS870S first I was really not amazed about the selectivity, also not about the quality of the build-in front end. But the filter-mod and also Kenwoods front-end-mod helped to solve these problems. But there was one additional possibility to improve something. When I reduced the output power to drive a bigger linear, I found, that the ratio is changing between SSB in comparison to modulate with a single-tone. If the percentage was 50% between voice and CW using 100W output before, the ratio is dropping down if you are running only 10W (measured with a peak-meter).
    That is not very helpful, because its not easy to drive the linear correctly in that case. And you cant improve that using higher microphone gain or processor. The reason is Kenwwods ALC-curcuit (its like the TS50S) which can be found on the RF-unit. In the curcuit diagram its named "Reserve Current Prevention". This part is directly controlling the TX-amplifier Q39. And this part has normally nothing to do with the power adjustment or regulation. But using lower output its more sensitive and therefor more effective.

    Turn your TS870 on its head (foots up) and remove the cover. If the display is looking into your direction, the big curcuit board on the left-hand-side (underneath an additional metallic shielding) is the RF-board. Remove all connections carefully and afterwards the complete board. There are 3 electrolyte capacitors named: C286, C287, C289. Place a small resistor (I used a small chip-resistor) with 1 KOhm in parallel to C289, which is in the middle. Best is to do that on the soldering side (not component side).
    Thats it ! Bring the TS870 back to live and afterwards you will see the improvment in SSB-mode and you can easily measure it. Everyone told me afterwards, pumping effects are gone and my voice sounds fresh and clear (is that possible with an age of 40 ?)
    If you are only running your rig with full output, its not neccesary to realize this mod. In my case I am going down to 5 Watts - afterwards I.$B!-.(Bm driving an attenuator going down to 20 mW (-24dB) and this is driving a commercial russian linear with the possibilty of 2KW out (+50dB). Therefor its absolutly necessary to have stable conditions.